Preparation of oxalates of metals of atomic number greater than 88



PREPARATION OF OXALATES OF METALS OF ATOMIC NUMBER GREATER THAN 88Robert B. Duiiield, Cilampaign, 111., assignor to the United States ofAmerica as represented by the United tates Atomic Energy Commission NoDrawing. Application December 10, 1948 Serial No. 64,711

Claims. (Cl. 260429.1)

This invention relates to oxalates of metals of atomic number greaterthan '88 and, more particularly, to a method for the preparation ofthese compounds. Specifically, this invention teaches a method for thepreparation of oxalates of metals such as thorium, plutonium and thelike.

Maslick and Wahl, in U. S. patent application, Serial Number 792,834,filed December 19, 1947, now Patent No. 2,833,800, granted May 6, 1958,have demonstrated a method for the preparation of heavy metal oxalates.Their method is directed, however, to the preparation of these compoundsfrom aqueous solutions and, specifically, to the preparation of theplutonium oxalate from solutions of plutonium and oxalate ions.

While plutonium trioxalate is a satisfactory and useful starting productin a scheme for the chemical purification of enriched fissionablematerials such as those used in homogeneous reactors and other neutronmultiplying systems, a rather cumbersome and time consuming procedurewas utilized in the past to achieve the end. Generally, this involvedchanging the valence state of one or more of the active materials andnumerous other chemical manipulations, as for example, extracting,washing, drying and the like. In this procedure as in any chemicalprocess, some of the invaluable materials are subject to loss in thevarious steps just described. Care must be taken to prevent even smalllosses of these materials,

not only because of their value but also because the the peroxide givesexcellent separation from light element impurities. It is to be pointedout, however, that plutonium peroxide is' a difiicult material toprocess. It is insoluble in dilute acids and even cold concentratednitric acid will not immediately begin to dissolve the peroxide cake.Once the mixture is heated in 5-16 molar nitric acid, the reactionbecomes quite vigorous. Large amounts of oxygen are liberated and thesolution foams in a manner that requires careful control measures, suchas the use of large reaction vessels, ice baths, spray traps, scrubbingtowers and the like. The temperature of the reacting mixture must bemaintained below 40 C. or uncontrolled foaming will occur, often withexplosive violence. Provision must be made for immediate'cooling of thevessel if vigorous foaming begins.

After the plutonium peroxide is dissolved, a number of additional stepsare necessary to obtain the plutonium in the form of the oxalate whichcan be readily converted by the proper process into a material suitablefor reduc- Hydrogen tion to the metal. The plutonium compound which isformed may be comprised of both plus four and plus six plutonium ions sohydrogen iodide solution, with or without intermediate steps, is addedto reduce the plutonium to the plus three valence state and aqueousoxalate solution is introduced into the water extract to precipitate theplutonium as the plus three oxalate. After removing the supernatant andwashing the precipitate with the appropriate solutions, the plus threeplutonium oxalate is obtained as a greenish-white, crystallineprecipitate.

While the foregoing procedure is very efiective for obtaining the plusthree plutonium oxalate from recovery solutions and residues, it is,nevertheless, a tedious and time consuming method. Since plutoniumperoxide is generally obtained as an intermediate product in therecovery method, a substantial saving of time and material could beeffected if the peroxide could be converted rapidly to an oxalate.

The present invention contemplates as the primary object, a rapid,efiicient, simple method for the preparation of an oxalate of a metal ofatomic number greater than 88, in the plus four valence state.

This invention contemplates as another object, a method for thepreparation of a substantially purified oxalate of a metal of atomicnumber greater than 88, in the plus four valence state.

This invention contemplates as another object, a method for thepreparation of a purified oxalate of a metal of atomic number greaterthan 88 from the corresponding metal peroxide.

This invention contemplates as another object, a method for thepreparation of thorium oxalate in' the plus four valence state.

This invention contemplates as another object, a method for thepreparation of purified thorium oxalate from thorium peroxide.

This invention contemplates as still another object, a a method for thepreparation of plutonium oxalate.

This invention contemplates as still another object, a a method for thepreparation of purified plus four plutonium oxalate from plutoniumperoxide.

Still further objects and advantages of this invention will becomeapparent to those skilled in the art from the description and exampleswhich follow.

In accordance with the above objects of the present invention, it hasbeen found that a satisfactory method of preparing an oxalate of a metalof atomic number greater than 88 is accomplished in the followingdescribed manner.

A peroxide of a metal of atomic number greater than 88 in thenon-dissolved state is treated with an aqueous acid solution containingoxalate ion, preferably aqueous oxalic acid solution, to yieldessentially a pure, insoluble oxalate of the corresponding metal in theform of large crystals. The reaction probably is as follows in which Mis the metal, having a valence of four:

The reaction is unique in that the metal peroxide appears to remain inthe insoluble state during the conversion to a solid metal oxalate.

After completion of the reaction, the products are treated in any mannerwell-known to those skilled in the arts to eliminate the supernatant,as, for example by filtration, decantation or centrifugation, and toretain the crystallized metal oxalate. The metal oxalate product isobtained in a quite pure form and only a minimum of washing is requiredafter separating the solid metal oxalate from the supernatant. Theprecipitate may be dried and stored or used wet in further chemicalprocessing. I

ae at In the prac ice of the present invention n as a specificembodiment thereof, the following example will serve to illustrate themethod employed in preparing the metal oxalat an to th s P rpose, ponium (element 9 4) is s ecte s the ex mpleof e etal of atom c num ergreater than 8- Example 1 Ten grams of plutonium peroxide in the solidstate are washed with 'three 5.-milliliter portions of 1 molar nitricacid to remove impurities such as the sulfate ion which may be p en as are l of p i ch m l processing. The material is then treated with 125milliliters of aqueous 0.67 molar oxalic acid solution which issufiic-ient to convert all the plutonium peroxide to p t n um oxalate nv o make h s pe n a o 9-2 m la i oxa i a The P se ce o an excess r acidi thoag to res t a mor complet metathe of t e P r id t the o alat by cit am un ti-impur s, su h s, r r ea t s; w ich il pr p a A 0.15 molarexcess of the acid corresponds to a solution ha ing a pH of bo 1 s he en u mix u permitted to digest for 3, hours at room temperature.Metathesis of the peroxide to the oxalate during this period results ina large crystalline form of the plus four plutonium oxalate, having anedge of about 22 microns. The supernatant is separated from theprecipitate by decanting or other well-known means and the oxalate iswashed with a 3.0 molar nitric acid solution containing 0.1 mole xa c act elim n te impu it e an to tain the precipitate in the more desirableform of large,

Purifi d c ys s- .A material balan on he p cts obtained by this methodshows an oxalation yield of 97.4 to 98.0 percent.

From the foregoing x mple it willhe s en h e method of this inventionoffers numerous advantages in the preparation of pure, crystalline,plutonium oxalate.

Th rystall n materia formed by thi method is very desirable in that itis obtained in practically theoretical y ld and is in a form su stantialy pu fi d fr m ll P s a d e dy fo f her processin o sto g In additio thesize of each indi idual c ysta s c d ably larger than is norm llyObtained by metathesis.

The following example illustrates a method by which thorium peroxide isconverted to thorium oxalate. While .a relatively small sampleis ,chosenfor illustration, the method is adequate for production on a largerscale.

Example II T n g ams of solid th um perox e e t ate with 190 millilitersof 0.67 molar ,oxalic acid solution at room temperature. Thiscorresponds to approximately 50 percent excess-of the acid and issufficient to insure complete oxalation. At room temperature, thereaction slow to start and a slig t appl ion of e is h pful ininitiating the metathesis. :Care must be taken .to avoid hot sp s in hre t ng mixture and for thi rea n, the use of a wat r bath is desirble.- Th m ure m y be stirred mechanically but air agitation ispreferred. In about 90 minutes, the metathesis is complete with amaximum temperature of .62 C. being attained. The mixture is permittedto stand and in about an hour welldefined square plates of thoriumoxalate are obtained. The supernatant is removed and the oxalatecrystals are washed twice with water and once with water containingoxalate ion. The thorium oxalate obtained after drying to remove theWater of crystallization is in the form of white, crystalline platesabout 1.0 microns ,on an edge and essentially free of all impurities.

Excellent yields of the oxalate are obtained by the method of thisinvention, being, for thorium oxalate, about 90 percent.

A further advantage of the method for this invention .is a definiteimprovement in the health and safety hazards of this method. Theelimination of the rapid decomposition of peroxides in the processdecreases the possibility of fir'e or explosion and losses to such anextent that the need for elaborate equipment such as large reactionvessels, ice baths, spray traps and the like is considerably lessened.

It is pointed out that the method of this invention can m td an ageouslybe u e in a schem f r h Purific ticn of p utoni m and oth m tal f atomnumber greater than 88, thus eliminating a portion of the complicatedand hazardous procedure heretofore employed to purify these heavyradioactive materials. As pointed out hereinbefore, a strongly acidsolution serves to eliminate the ext-precipitation as oxalate of therare earths which are regarded as being most harmful with respect toslow neutron absorption.

Although the invention has been described in detail as applying to thepreparation of plutonium and thorium oxalates, it is equally applicable,with minor modifications, to the preparation of insoluble oxalates ofother heavy metals having an atomic number of 89 or above. The processis applicable. not only to the natural isotopic mixture of the elementsbut also to the. individual isotopes such as uranium 235, uranium 23.8,plutonium 238, plutonium 239., and the like.

Since many embodiments of this invention are possible it is to beunderstood that this invention is not to be limited except as indicatedin the appended .claims.

What is claimed is:

l. A :method for the preparation of heavy metal oxalates which comprisesreacting in the solid state a peroxide of a heavy metal having an atomicnumber greater han .88 with :annq-ueous,v acidic oxalate solution toform an insoluble heavy metal oxalate.

,2. A method for the preparation of insoluble heavy metal oxalates whichcomprises contacting in the solid state insoluble peroxide of a heavymetal having an atomic number greater than .88 with an aqueous oxalicacid solution for a period of time sutficient to convert substantiallyall the heavy metal peroxide to the oxalate, and separating theresulting insoluble lower valent heavy metal oxalate formed from thesupernatant.

3. A method for the preparation of thorium oxalate which comprisesreacting thorium peroxide in the Solid state with an aqueous acidoxalate solution to form in? soluble thorium oxalate as large, purifiedcrystals.

4. A method for the preparation .of-insoluble thorium oxalate whichcomprises treating insoluble thorium peroxide with an aqueous oxalicacid solution for at least 3 hours at room temperature, and separatingsolid thorium oxalate from the supernatant in the form of well-definedcrystals.

5. A method for the preparation of insoluble thorium oxalate whichcomprises reacting insoluble thorium per, oxide with a 50 percent excessof 0.67 molar oxalic acid solution -for a period of time suffic-ient toconvert sub. stantially all the peroxide to the oxalate and separatingthe insoluble thorium oxalate from the supernatant in the form ofwell-defined homogeneous crystals.

6. A method for the preparation of insoluble thorium oxalate whichcomprises contacting 10 grams of thorium peroxide with about 19-0milliliters of 0.67 molar oxalic acid solution at room temperature,digesting the mixture for at least 3 hours to obtain the insolublethorium oxalate substantially free of contaminating impurities andseparating the well-defined homogeneous thorium oxalate crYStals fromthe supernatant.

7. A method for the preparation of plutonium oxalate which comprisesreacting plutonium peroxide in the solid state with an aqueous acid.oxalate solution to form insoluble plutonium peroxide as large purifiedcrystals.

8. A method for the preparation of insoluble plutonium oxalate whichcomprises treating insoluble plutonium peroxide with an aqueousoxalicacid solution .for at least s h s at temperature, :and separating. olidplutonium oxalate from the supernatant in the form of large,well-defined crystals.

9. A method for the preparation of insoluble plutonium oxalate whichcomprises reacting insoluble plutonium peroxide with a 50 percent excessof 0.67 molar oxalic acid solution for a period of time sufficient toconvert substantially all the peroxide to the oxalate and separating theinsoluble plutonium oxalate from the supernatant in the form ofwell-defined homogeneous crystals.

10. A method for the preparation of insoluble plutonium oxalate whichcomprises contacting 10 grams of plutonium peroxide with about 125milliliters of 0.67 molar oxalic acid solution at room temperature,digesting the mixture for at least 3 hours to obtain the insolubleplutonium oxalate substantially free of contaminating impurities andseparating the well-defined homogeneous plutonium oxalate crystals fromthe supernatant References Cited in the file of this patent UNITEDSTATES PATENTS Thews Feb. 17, 1925 OTHER REFERENCES Accum: A PracticalEssay on Chemical Reagents or Tests, p. 68 (1817), publ. by M. Carey 8:Son, Philadelphia, Pa.

1. A METHOD FOR THE PREPARATION OF HEAVY META OXALATES WHICH COMPRISESREACTING IN THE SOLID STATE A PER OXIDE OF A HEAVY METAL HAVING ANATOMIC NUMBER GREATER THAN 88 WITH AN AQUEOUS ACIDIC OXALATE SOLUTION TOFORM AN INSOLUBLE HEAVY METAL OXALATE.